Polymer compositions and cast films

ABSTRACT

Polypropylene impact copolymer compositions are provided which contain a homopolymer phase of predominantly homopolymeric polypropylene, a copolymer phase of copolymerized ethylene and propylene, and a nucleating agent. The inventive compositions have a rubber content (Fc) in the range of 25 to 45% by weight, a crystallization temperature in the range of 122° to 132° C., a melt flow in the range of about 7 to about 60 dg/min, and a ratio of the intrinsic viscosity of the copolymer phase to the intrinsic viscosity of the homopolymer phase of 1.4 to about 1.9. The polypropylene impact copolymer compositions may be used to form cast films which preferably are soft, quiet, and suitable for use in products to be used next to the skin, such as diapers, adult incontinence pads and feminine hygiene products.

FIELD OF THE INVENTION

The invention relates generally to polymer compositions and cast filmsproduced with such polymer compositions. More particularly, theinvention relates to polypropylene impact copolymer compositionscontaining a nucleating agent and having specified characteristics ofrubber content (Fc), crystallization temperature, melt flow and ratio ofintrinsic viscosity of the copolymer phase to the intrinsic viscosity ofthe homopolymer phase. The invention also relates to processes formaking such polymer compositions and cast films. The polymercompositions according to the invention have characteristics suitablefor the formation of soft, quiet cast films which may be employed inproducts to be used against the skin, such as diapers, adultincontinence pads and feminine hygiene products.

BACKGROUND OF THE INVENTION

Polypropylene compositions have traditionally been used to make filmproducts. However, problems have been associated with the processabilityof polypropylene compositions and the film products containing suchpolypropylene compositions. For example, in the production of castfilms, extruded polypropylene melts often stick to the chill roll, whichresults in reduced production yield and efficiency. Polypropylene filmproducts, particularly those from polypropylene homopolymers, arerelatively brittle and have low impact resistance. These filmcharacteristics create disadvantages of unpleasant texture, excessivenoise and susceptibility to tearing.

Numerous procedures have been proposed for modifying the properties ofthe polypropylene homopolymers to improve their characteristics. Many ofthose proposals have involved incorporating a propylene/α-olefincopolymer portion in an otherwise homopolymeric polypropylene. Thestructure of such modified polypropylene polymers is variable, butsomewhat uncertain.

For example, Leibson et al., U.S. Pat. No. 3,514,501, describes aprocess for the production of block copolymers wherein a homopolymericpolypropylene prepolymer is produced and a block of at least one α-olefnis grown from the prepolymer in a second polymerization step. Anotherapproach involves the mixing of a polypropylene homopolymer with apropylene/ethylene copolymer. Most commercial products of high impactstrength result from the production of a first polymer, usually apolypropylene homopolymer, and the production of a copolymeric portionin the presence of the initial polymer product mixture which stillcontains active polymerization sites. Whether the resulting product is atrue block copolymer, a mixture of homopolymer and copolymer or is ofanother structure is not entirely clear. They are often referred to as"polypropylene impact copolymers," regardless of the precise nature oftheir structure. Polypropylene impact copolymers are said to contain ahomopolymer phase and a copolymer phase. The homopolymer phase is oftenhomopolymeric polypropylene and the copolymer phase is often a rubbercomposition.

McCullough, Jr. et al., U.S. Pat. No. 5,362,782, describes stresswhitening resistant polypropylene impact copolymer compositions whichcontain a homopolymer phase of at least 94% polypropylene, a copolymerphase of propylene and ethylene, and a nucleating agent, wherein theratio of the intrinsic viscosity of the copolymer rubber phase to theintrinsic viscosity of the homopolymer phase is from about 1.1 to about1.3. McCullough, Jr. et al., U.S. Pat. No. 5,250,631, describes morestress whitening resistant polypropylene impact copolymer compositionswhich contain a homopolymeric phase of predominantly homopolymericpolypropylene and a terpolymer phase having a major proportion ofethylene, a minor proportion of an α-olefin of at least 4 carbon atomsand a minor proportion of propylene. Neither of these references refersto polypropylene compositions to be used in the production of soft,quiet films.

Other references including Sumitomo, U.S. Pat. No. 3,517,086; Sumitomo,U.S. Pat. No. 4,902,738; and El Paso, U.S. Pat. No. 4,704,421, discusspolymeric compositions which may be used to produce films that are"soft." However, none of these references refer to a polypropyleneimpact copolymer containing a nucleating agent and having a rubbercontent (Fc) of greater than 25 % by weight.

A need exists in the art of polymer compositions and cast films forpolypropylene polymer compositions having good processability andcharacteristics sufficient to produce soft, quiet east films.

SUMMARY OF THE INVENTION

The invention provides novel polymer compositions and cast filmsproduced with such polymer compositions. More particularly, theinvention relates to polypropylene impact copolymer compositionscontaining a nucleating agent and having specified characteristics ofrubber content (Fc), crystallization temperature, melt flow and ratio ofintrinsic viscosity of the copolymer phase to the intrinsic viscosity ofthe homopolymer phase. The invention also relates to processes formaking such polymer compositions and cast films. In a preferredembodiment, the polymer compositions according to the invention havegood processability and are used to produce cast films having desirableproperties. The cast film products according to the invention areparticularly useful in applications requiring a soft, quiet filmincluding products to be used against the skin, such as diapers, adultincontinence pads and feminine hygiene products.

In a preferred embodiment, the inventive polymer compositions arepolypropylene impact copolymer compositions having a rubber content (Fc)of about 25 to about 45% by weight, a nucleation level characterized bya crystallization temperature in the range of 122°-132° C., a melt flowof about 7 to about 60 dg/min, and a ratio of the intrinsic viscosity ofthe copolymer phase to the intrinsic viscosity of the homopolymer phaseof 1.4 to about 1.9.

In a further preferred embodiment, the polypropylene impact copolymercompositions are used to produce east films. The cast films according tothe invention preferably have a tensile modulus (1% secant) of less than100,000 psi (both machine direction (MD)) and transverse direction(TD)), an Elmendorf tear strength greater than 60 g/mil (MD) and a Dartdrop impact strength of greater than 1200 inch-gram, as measured forcast films produced from polypropylene impact copolymers having a meltflow of 8 to 12 dg/min. For cast films produced from polypropyleneimpact copolymers having higher melt flows, the range of preferredElmendorf tear strength and Dart drop impact strength includes lowervalues.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of the effect of rubber content (Fc) on the tensilemodulus (1% secant) of nucleated polypropylene impact copolymer castfilm.

FIG. 2 is a graph of the effect of rubber content (Fc) on the Elmendorftear strength of nucleated polypropylene impact copolymer cast film.

FIG. 3 is a graph of the effect of rubber content (Fc) on the Dart dropimpact strength of nucleated polypropylene impact copolymer cast film.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The polymer compositions of the present invention are polypropyleneimpact copolymer compositions comprising a homopolymer phase of at least94 % homopolymerized polypropylene, a copolymer phase comprising acopolymer of ethylene and propylene, and a nucleating agent, wherein thepolypropylene impact copolymer composition has a rubber content (Fc) ofabout 25 to about 45 % by weight, a crystallization temperature of about122°-132° C., a melt flow of about 7 to about 60 dg/min, and a ratio ofthe intrinsic viscosity of the copolymer phase to the intrinsicviscosity of the homopolymer phase of 1.4 to about 1.9.

The homopolymer phase in the polypropylene impact copolymer according tothe invention is predominantly homopolymeric polypropylene. To obtainparticular properties for particular applications it may be desirable toincorporate in the otherwise homopolymer portion of the impact copolymercompositions a small amount, e.g., up to about 6% by weight, of a secondα-olefin having up to 4 carbon atoms inclusive, such as ethylene or1-butene. The incorporation of the optional small amounts of secondα-olefin is by conventional methods and serves to modify but notsubstantially alter the properties of the homopolymer phase. In theembodiments where a small mount of second α-olefin is incorporated,although technically a copolymer, the product is still referred to asthe homopolymer phase. The optional second α-olefn is preferablyethylene, preferably incorporated in an amount up to about 2 % byweight, with from about 4% by weight to about 6% being more preferred.However, the homopolymer phases which are substantially homopolymericpolypropylene, i.e., phases produced in the substantial absence ofsecond α-olefin, are preferred.

The copolymer phase, or rubber phase, is a copolymer of ethylene andpropylene. Preferably, the ethylene content of the copolymer phase is inthe range of 50 to 65% by weight, and more preferably in the range of 55to 60% by weight.

The nucleating agent may include aromatic carboxylic acids and theirderivatives, e.g. sodium benzoate, aluminum p-tert-butyl benzoate andaluminum benzoate; metal organic phosphates, e.g. sodiumdi(4-t-butylpbenyl)phosphate and sodium 2,2'-methylenebis(4,6-di-tertiary-butylphenyl)phosphate; benzylidene sorbitolderivatives; talc; polyvinyl cycloalkanes, e.g. polyvinyl cyclohexane;and certain organic dicarboxylic acid derivatives, e.g. sebacic acid.Nucleating agents allow the polymers to be crystallized at a highertemperature during film forming operations. The addition of thenucleating agent to the polypropylene impact copolymer also increasesthe stiffness of the film product.

In a preferred embodiment, the nucleating agent employed in theinvention is sodium benzoate. Sodium benzoate may be added to thepolypropylene impact copolymer in an mount in the range of 50 to 5000ppm, and preferably in the range of 500 to 1500 ppm. In a furtherpreferred embodiment the sodium benzoate has a mean particle size underabout 5 μm, and preferably in the range of about 0.5 to about 3 μm.Sodium benzoate may also act as an acid acceptor, which eliminates theneed to add a further acid acceptor component to the polymer compositionwhen sodium benzoate is employed as the nucleating agent.

The characteristics of the polypropylene impact copolymer compositionsaccording to the invention are generally sufficient to produce quiet,soft films. The inventive films are also preferably characterized asflexible, conformable, resistant to tearing and having goodprocessability.

The rubber content (Fc) of the polymer composition is preferably about25 to about 45% by weight, and more preferably between about 30 to about38 % by weight. For purposes of the present invention, the value of Fcis determined by conventional Fourier transform infrared spectroscopyanalysis (FTIR). The relatively high rubber content provides thedesirable softness characteristic of the films according to theinvention.

The crystallization temperature of the polypropylene impact copolymersaccording to the invention generally reflects the type and concentrationof the nucleating agent added to the composition. Preferably thecrystallization temperature of the polypropylene impact copolymercompositions of the invention is in the range of 122° to 132° C. Morepreferably, when the nucleating agent is sodium benzoate, thecrystallization temperature of the polypropylene impact copolymercompositions of the invention is in the range of 124° to 130° C. Thecrystallization temperature is determined by melting a polymer sample at220° C. in a differential scanning calorimeter (DSC), Perkin ElmerSeries 7, then cooling the sample at 10° C. per minute. The peaktemperature of the crystallization temperature is then reported as thecrystallization temperature (Tc).

The melt flow of the polypropylene impact copolymer according to theinvention is in the range of about 7 to about 60 dg/min. In a preferredembodiment, the melt flow of the polypropylene impact copolymer is inthe range of 8 to 12 dg/min. Where a film is made from a polymercomposition according to the invention having a melt flow in the rangeof 8 to 12 dg/min, that film has a relatively high tensile elongation atbreak, preferably the range of 600 to 800% in MD and slightly lower inTD. In another preferred embodiment, the melt flow of the polypropyleneimpact copolymer is in the range of 28 to 32 dg/min. The melt flowcharacteristic may be determined by a conventional test procedure, suchas ASTM-1238 Cond. L.

The ratio of the intrinsic viscosity of the copolymer phase to theintrinsic viscosity of the homopolymer phase is preferably in the rangeof 1.4 to about 1.9, and more preferably in the range of 1.5 to 1.7. Theterm intrinsic viscosity as used herein is used in its conventionalsense to indicate the viscosity of a solution of a material, in thiscase a solution of a polymer, in a given solvent at a given temperature,when the polymer composition is at infinite dilution. According to theASTM standard test method D 1601-78, its measurement involves a standardcapillary viscosity measuring device, in which the viscosity of a seriesof concentrations of the polymer in the solvent at the given temperatureare determined. In the case of the polymers of the present invention,decalin (decahydronaphthalene) is an illustrative suitable solvent and atypical temperature is 135° C. From the values of the viscosity ofsolutions of varying concentration, the "value" at infinite dilution canbe determined by extrapolation. In the case of the present polypropyleneimpact copolymers, the homopolymer portion is initially produced and theintrinsic viscosity of that portion is measured directly. The intrinsicviscosity of the copolymer portion cannot be measured directly. Theintrinsic viscosity of the total polypropylene impact copolymer productis determined and the intrinsic viscosity of the copolymer portion iscalculated as the quotient of the intrinsic viscosity of the totalpolypropylene impact copolymer ( η!whole) less the fraction ofhomopolymer times its intrinsic viscosity ( η!homo), all divided by thefraction of the total impact copolymer which is copolymer. The formulais ##EQU1## In this formula, Fc is stated in terms of a fraction ofethylene/propylene copolymer in the total polypropylene impact copolymer(instead of as a percentage as in the remainder of the specification andclaims). This fraction is determined by conventional procedures,including infrared analysis.

The polymer compositions of the invention may be prepared by methodsemploying conventional polymerization techniques, such as theZiegler-Natta polymerization technique. The polymer compositions may beproduced, for example, in a two-step gas phase process which is broadlyconventional. For example, the polymerization process of the inventionmay be conducted in a gas phase in the presence of a stereoregularolefin polymerization catalyst. Such catalysts are broadly conventionaland are employed in the polymerization of α-olefins of three or morecarbon atoms to produce stereoregular products. In terms conventionallyemployed to describe such catalysts, the stereoregular catalysts of highcatalytic activity contain as a first constituent a procatalyst which isa titanium-containing solid, usually a titanium halide-containing solid,and which often contains an electron donor such as an aromatic ester.Suitable electron donors which may be used in the preparation of thesolid catalyst component are ethers, esters, ketones, phenols, amines,amides, imines, nitriles, phosphines, phosphites, stilbenes, arsines,phosphoramides and alcoholates. The electron donors may be used singlyor in combination. Preferred electron donors for use in preparing thetitanium constituent are ethyl benzoate and diisobutyl phthalate. Thesecond catalyst constituent, termed a co-catalyst, is an organoaluminumcompound which may be partly or totally complexed with the thirdcatalyst constituent, conventionally termed a selectivity control agent.Aromatic esters, amines, hindered amines, esters, phosphites,phosphates, aromatic diesters, alkoxy silanes, aryloxy silanes, silanes,hindered phenols and mixtures thereof may be useful as the selectivitycontrol agent in the inventive process.

Such stereoregular olefin polymerization catalysts are described innumerous patents and other references including Nestlerode et al., U.S.Pat. No. 4,728,705. Although a variety of chemical compounds are usefulas the constituents of the polymerization catalysts, a typicalstereoregular olefin polymerization catalyst contains as procatalyst asolid comprising a magnesium halide, a titanium halide and an electrondonor such as ethyl benzoate. The halide moieties of such procatalystsare customarily chloride moieties. The co-catalyst is typicallytriethylaluminum or tri-isobutylaluminum which is often at leastpartially complexed with an aromatic ester such as ethylp-ethoxybenzoate, ethyl p-methoxybenzoate or methyl p-methylbenzoate asthe selectivity control agent, or a silane such as diisobutyl dimethoxysilane. Use of the catalysts of this type results in a stereoregularpolymeric product when olefins of three or more carbon atoms arepolymerized and many of the catalysts are recognized as high activitycatalysts which are able to produce polymers of desirable propertieswithout the necessity of removing catalyst residues in a de-ashing step.

These catalyst are used in established processes to polymerize orcopolymerize α-olefins. The processes may employ a liquid,non-polymerizable diluent or alternatively may employ as liquid diluenta monomer to be polymerized. To produce the impact copolymers of theinvention, however, it is desirable to utilize a gas phase process. Anumber of gas phase polymerization processes are available but one suchprocess which is illustratively and suitably used to produce the impactcopolymer products of the invention is described by Goeke et al, U.S.Pat. No. 4,379,759, which is incorporated herein by reference.

A gas phase process is typically operated by charging to a suitablereactor an amount of preformed polymer particles and lesser amounts ofcatalyst components. The gaseous olefin or olefins to be polymerized arepassed through the bed of particles under polymerization conditions oftemperature and pressure sufficient to initiate polymerization. Uponpassing through the particle bed the unreacted gas is withdrawn from thereactor and recycled together with make-up feed gas. As the catalyst islost through incorporation of minute amounts of catalyst within thepolymer product, additional catalyst is provided to the reactor, oftenthrough the use of an inert transport gas such as nitrogen or argon. Thereaction temperature is selected to be below the sintering temperatureof the polymer particles and is controlled by an external heat exchangerin the gas cycle. Reaction temperatures from about 30° C. to about 120°C. may be used with reaction temperatures from about 50° C. to about 90°C. being more commonly used. The reaction pressure is generally up toabout 1000 psi with pressures from about 100 psi to about 400 psi beingpreferred. The precise control of reaction conditions as well as theaddition of catalyst and feed gas and the recycle rate of unreactedmonomer is within the skill of the art.

An additional means of reaction and product control is achieved by theprovision for the addition of molecular hydrogen to the reactor and thusthe polymerization system. The addition of molecular hydrogen serves tocontrol the molecular weight of the product, most likely by functioningas a chain transfer agent. Control of molecular weight of the polymericproduct also in part determines the intrinsic viscosity and melt flow ofthe product. The use of hydrogen to control polymer molecular weight andthus product intrinsic viscosity and melt flow is also within the skillof one in the art.

The desired polymer products are obtained as particulate matter formedby growth of polymer product on the polymer particles provided to thefluidized bed or as particles formed in the reactor. The productparticles are removed from the reactor at a rate which is substantiallyequivalent to the rate of polymer production and said particles arepassed to a subsequent reaction zone or are finished by conventionalmethods prior to use.

It is conceivable, although impractical, to produce the impactcopolymers of the invention in a single reactor by control of thecomposition of feed gas and recycle of unreacted monomer and polymericproduct. However, it is more common to operate the gas phase process forthe production of the compositions of the invention in a two-stageprocess wherein each stage operates in the gas phase in a separatereactor. In such a modification, the homopolymer portion of the impactcopolymer is initially produced as described above in a suitable gasphase reactor which generally but not necessarily employs hydrogen tocontrol the molecular weight of the product and thus the intrinsicviscosity and melt flow of this product.

This initial homopolymer product containing active catalyst sites isthen passed to a second gas phase reactor containing a second fluidizedbed. A portion of unreacted monomer from the initial polymerization stepis also passed to the second reactor, also containing a second fluidizedbed, together with the monomers to be employed in the production of thecopolymer phase. The production of copolymer or rubber phase takes placein the second reactor where it may also be desirable to providemolecular hydrogen to control molecular weight and thus intrinsicviscosity and melt flow.

The product of the second polymerization is a polypropylene impactcopolymer which generally is in a powder form. An appropriate mount ofnucleating agent, such as sodium benzoate, is added to the powderpolypropylene impact copolymer. Other components may be added to thefilm forming composition or resin. For example, pigment, anti-oxidants,acid acceptors, processing stabilizers, fillers, etc., may beincorporated in amounts up to about 10% of the weight of the filmwithout detrimentally affecting the film properties. The powder polymercomposition may then be extruded into pellets.

The polypropylene impact copolymer composition according to theinvention may be used to form a film, preferably a cast film. Thepolypropylene impact copolymer composition, generally in pelletizedform, is fed into an extruder. The molten polymer is extruded through aslot extrusion die onto a chill roll to cool the polymer melt to a solidfilm. Due to the inherent polymer or resin characteristics, the filmproduct will have both suitable softness and quietness. Theprocessability is also enhanced by the polymer or resin characteristicsas the film-forming composition is not likely to stick to the chillroll, even at relatively high processing rates.

The resulting film can be treated by any one or more known postextrusion techniques including corona treatment, flame treatment andultraviolet irradiation. The film product may also be edge trimmed, slitinto sheets or collected on a roll.

The following example is provided so as to enable those of ordinaryskill in the art to make the compositions of the invention. Theseexamples are not intended to limit the scope of what the inventorregards as his invention. Efforts have been made to ensure accuracy withrespect to numbers used to characterize the measured conditions;however, some experimental errors and deviations may be present.Accordingly, departures may be made from the detail without departingfrom the spirit or scope of the disclosed general inventive concept.

EXAMPLE

Production of Cast Film Having High Rubber Content

For initial powder-to-pellet compounding, polypropylene impact copolymerpowders of varying rubber content (Fc) were used. The unstabilizedpolypropylene impact copolymer powder was compounded with Irganox 1010(phenolic antioxidant) (750 ppm), Sandostab P-EPQ (phosphoniteprocessing stabilizer) (750 ppm) and nucleating agent sodium benzoate(1000 ppm). The sodium benzoate had a me, an particle size ofapproximately 2 μm. The polypropylene impact copolymer powder and theadditives were extruded into pellets under nitrogen using a 11/4 inchBrabender extruder with Maddock mixing screw and 250° C. melttemperature.

The pellets of nominal eleven (11) melt flow (MF) were extruded intocast film (1 mil thick), using a 3/4 inch Brabender extruder at 240° C.melt temperature, 8 inch wide slot die and Killion chill roll (17° C.).

The mechanical properties of the films were then tested at 23° C.according to the following ASTM procedures: tensile modulus (1% secant)by D-882 using an Instron tester at 12.7 cm/min crosshead speed;Elmendorf tear strength by D-1922; Dart drop impact strength by D-3029.For tensile and tear, both machine direction (MD) and transversedirection (TD) properties were measured. The films of 25-35% Fc had lowtensile modulus (less than 100,000 psi in MD or TD), high Elmendorf tearstrength and high Dart drop impact strength. The films had a hightensile elongation at break of 600 to 800% in MD and a slightly lowerrange at TD.

FIGS. 1-3 present a summary of the effect of rubber content on tensilemodulus (1% secant) (FIG. 1), Elmendorf tear strength (FIG. 2) and Dartdrop impact strength (FIG. 3) for nucleated polypropylene polymer impactcompositions prepared according to the Example.

What is claimed is:
 1. A propylene impact copolymer compositioncomprising:a homopolymer phase of at least 94% homopolymericpolypropylene, a copolymer phase comprising a copolymer of ethylene andpropylene, and a nucleating agent comprising sodium benzoate, whereinthe polypropylene impact copolymer composition has a rubber content (Fc)of about 25 to about 45%, a crystallization temperature of 122° to 132°C., a melt flow of about 7 to about 60 dg/min measured according toASTM-1238, condition "L" and a ratio of intrinsic viscosity of thecopolymer phase to the intrinsic viscosity of the homopolymer phase of1.4 to about 1.9; and wherein the copolymer phase is produced in thepresence of the homopolymeric polyproylene.
 2. A composition accordingto claim 1, wherein the copolymer phase contains about 50 to about 65 %by weight ethylene.
 3. A composition according to claim 1, wherein thesodium benzoate nucleating agent is present in an amount between 50 and5000 ppm.
 4. A composition according to claim 1, wherein the sodiumbenzoate nucleating agent is present in an amount between 500 and 1500ppm.
 5. A composition according to claim 4, wherein said sodium benzoatehas a mean particle size of 0.5 to 3 μm.
 6. A film comprising:apropylene impact copolymer composition comprising a homopolymer phase ofat least 94% homopolymeric polypropylene, a copolymer phase comprising acopolymer of ethylene and propylene, and a nucleating agent comprisingsodium benzoate, wherein the polypropylene impact copolymer compositionhas a rubber content (Fc) of about 25 to about 45%, a crystallizationtemperature of 122° to 132° C., a melt flow of about 7 to about 60dg/min measured according to ASTM-1238, condition "L" and a ratio ofintrinsic viscosity of the copolymer phase to the intrinsic viscosity ofthe homopolymer phase of 1.4 to about 1.9; and wherein the copolymerphase is produced in the presence of the homopolymeric polyproylene. 7.A film according to claim 6, wherein the tensile modulus (MD and TD) ofthe film is less than 100,000 psi.
 8. A film according to claim 6,wherein the Elmendorf tear strength (MD) of the film is greater than 60grams per mil.
 9. A film according to claim 6, wherein the Dart dropimpact strength is greater than 1200 inch-gram.
 10. A film according toclaim 6, wherein the copolymer phase contains about 50 to about 65% byweight ethylene.
 11. A film according to claim 6, wherein the melt flowof the polypropylene impact copolymer composition is 8 to 12 dg/min. 12.A film according to claim 4, wherein the tensile elongation (MD) atbreak is 600-800%.
 13. A process comprising:mixing a nucleating agentcomprising sodium benzoate and a propylene impact copolymer to form anucleated polypropylene impact copolymer wherein said polypropyleneimpact copolymer comprises a homopolymer phase of at least 94%homopolymeric polypropylene, a copolymer phase comprising a copolymer ofethylene and propylene, wherein the nucleated polypropylene impactcopolymer composition has a rubber content (Fc) of about 25 to about45%, a crystallization temperature of 122° to 132° C., a melt flow ofabout 7 to about 60 dg/min measured according to ASTM-1238, condition"L" and a ratio of intrinsic viscosity of the copolymer phase to theintrinsic viscosity of the homopolymer phase of 1.4 to about 1.9; andwherein the copolymer phase is produced in the presence of thehomopolymeric polyproylene.
 14. A process according to claim 13, whereinsaid sodium benzoate has a mean particle size of 0.5 to 3 μm.
 15. Aprocess according to claim 13, wherein the amount of sodium benzoatenucleating agent mixed with the polypropylene impact copolymer isbetween 50 and 5000 ppm.
 16. A process according to claim 13, whereinthe amount of sodium benzoate nucleating agent mixed with thepolypropylene impact copolymer is between 500 and 1500 ppm.
 17. Aprocess for forming a cast film comprising:mixing a nucleating agentcomprising sodium benzoate and a propylene impact copolymer to form anucleated polypropylene impact copolymer wherein said nucleatedpolypropylene impact copolymer comprises a homopolymer phase of at least94% homopolymeric polypropylene, a copolymer phase comprising acopolymer of ethylene and propylene, wherein the nucleated polypropyleneimpact copolymer composition has a rubber content (Fc) of about 25 toabout 45%, a crystallization temperature of 122° to 132° C., a melt flowof about 7 to about 60 dg/min measured according ASTM-1238, condition"L" and a ratio of intrinsic viscosity of the copolymer phase to theintrinsic viscosity of the homopolymer phase of 1.4 to about 1.9; andextruding the nucleated polypropylene impact copolymer to form a castfilm; and wherein the copolymer phase is produced in the presence of thehomopolymeric polyproylene.
 18. A process according to claim 17, whereinsaid sodium benzoate has a mean particle size of 0.5 to 3 μm.
 19. Aprocess according to claim 17, wherein the mount of sodium benzoatenucleating agent mixed with the polypropylene impact copolymer isbetween 50 and 5000 ppm.
 20. A process according to claim 17, whereinthe amount of sodium benzoate nucleating agent mixed with thepolypropylene impact copolymer is between 500 and 1500 ppm.
 21. Acomposition according to claim 1 additionally comprising at least onecomponent selected from the group consisting of: pigment, antioxidant,acid acceptor, processing stabilizer or filler.
 22. A compositionaccording to claim 21 wherein the antioxidant is a phenolic antioxidant.23. A composition according to claim 21 wherein the processingstabilizer is a phosphonite processing stabilizer.
 24. A compositionaccording to claim 1 wherein the homopolymeric polypropylene phase isproduced in a first reactor and is passed to a second reactor whereinthe copolymer phase is produced.